Implementation of a two-stream-fan in the CIRSTEL system

[摘要] This thesis describes the design and incorporation of a twin-stream fan into the CIRSTEL tailboom. The Combined Infra-Red Suppression and Tail rotor Elimination (CIRSTEL) tail boom is asystem designed to replace the tail rotor on a conventional helicopter. It relies on the Coanda effectto create circulation around the helicopter tail boom when exposed to the rotor downwash. Thisgenerates sideways-directed lift to counter the main rotor torque, and a tail thruster adds extratorque and directional control. A twin-stream fan supplies separate air streams to each of theCoanda and tail thruster sections. The first section of the study describes the experimental testsdone on an 83% scale demonstrator of the twin-stream fan with the objective to verify the conceptand determine the fan section efficiencies. Subsequent modifications done to the fan stator bladesare also evaluated. The efficiencies of the design were shown to exceed the targets in bothsections. The section concludes with design recommendations for a future fan, based on thefindings of the experiments. A brief analysis of the CIRSTEL system is presented and by usingoptimisation techniques the predicted power demand of the system could be significantly reducedfrom a conventional tail rotor. The second section of the study details the conceptual design andCFD evaluation of air intakes for the fan that can be fitted to the helicopter. The objective here wasto study the flow affecting helicopter intakes as well as to establish design considerations for a fanintake. A basic intake concept was developed for the Alouette III/CIRSTEL combination andmodified according to results based on the CFD simulations. The intake design was evolved to thepoint were it was shown that the concept is feasible. These CFD simulations were an initial effortto design the fan intakes with the help of a simplified rotor flow field. The investigation wassubsequently extended to investigate helicopter intake design considerations in the presence of arepresentative rotor, which was modelled as an actuator disk in the CFD simulations. In thisinvestigation top and side mounted intake concepts were compared and analysed for suitability as afan intake. Each intake concept showed its own advantages. Due to the proximity of the rotor hubto the intake, distortion and total pressure levels at the fan face are influenced negatively. Thereport is concluded with design recommendations for the intake as applied to the currentAlouette III configuration, as well as for implementation on helicopters in general.

[发布机构] Stellenbosch University